The entire disclosure of Japanese Patent Application No. Hei 11-341194 filed on Nov. 30, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a method for producing a thermoelectric semiconductor and, more particularly, to a method for producing a thermoelectric semiconductor including plastic deformation of the thermoelectric semiconductor.
2. Description of Related Art
As a thermoelectric semiconductor used for an electric cooling device or a thermoelectric transducer, a material having a hexagonal crystal structure is often used. The thermoelectric semiconductor of such a material is produced as variety of material structures, for example a single crystal structure, a polycrystal structure, a sintering structure, and so on.
The single crystal structure shows high performance (hereinafter referred as xe2x80x9cFigure of Meritxe2x80x9d) due to complete crystal orientation. However, the material of a single crystal structure has a low mechanical strength and is fragile, due to existence of cleavage planes (hereinafter referred as xe2x80x9cc-planesxe2x80x9d) arranged in parallel to the crystal structure. The material having a polycrystal structure, which is produced by a one directional solidified method such as the Bridgeman method, has a moderate performance and moderate mechanical strength. The material of a sintering structure, which is produced by sintering crystal powders, has a low performance but shows high mechanical strength. One of these materials is selected with consideration of the using environment, condition and so on.
The thermoelectric semiconductor is produced as an ingot of the thermoelectric semiconductor material. The ingot is sliced to form wafers. A wafer is diced to form a thermoelectric semiconductor chip (i.e. a thermoelectric semiconductor element). In view of the mass-production, it is more efficient to slice a large ingot to make many wafers at one time, rather then to slice a small ingot. However, the large ingot has variations in performance because the temperature dispersion and pressure dispersion are large at the ingot production step. On the contrary, the small ingot has a uniform performance, but the small ingot causes a reduction of productivity.
Accordingly, an object of this invention is to solve above conventional problems.
Further, another object of this invention is to produce a large ingot of the electric semiconductor having uniform performance in any portion therein.
According to a feature of the invention, the above and other objects are achieved by a method for producing a thermoelectric semiconductor, which includes an ingot producing step for producing an ingot of the thermoelectric semiconductor, and an integrating step for integrating a plurality of the ingots by plastic deformation so as to produce an integrated ingot for the thermoelectric semiconductor.
The advantages of the aforementioned features of this invention include the feature that a plurality of ingots are integrated to form an integrated ingot in the integrating step. Therefore, the ingot becomes large by the integrating step and many wafers can be produced at one time in the slicing step so that the productivity is improved. Further, the connecting strength at the connecting interface is strengthened by the plastic deformation and therefore the mechanical strength of the integrated ingot is improved. Furthermore, orientation of the C-planes in the sintered semiconductor material is improved by the plastic deformation and therefore the thermoelectric performance (Figure of Merit) is also improved.